Mesozoic-Cenozoic mafic magmatism in Sanandaj-Sirjan Zone, Zagros Orogen (Western Iran): Geochemical and isotopic inferences from Middle Jurassic and Late Eocene gabbros
Mesozoic-Cenozoic mafic magmatism in Sanandaj-Sirjan Zone, Zagros Orogen (Western Iran): Geochemical and isotopic inferences from Middle Jurassic and Late Eocene gabbros
复制标题
DOI：
10.1016/j.lithos.2017.05.009
复制
发表时间：
2017-07
期刊：
影响因子：
3.5
通讯作者：
R. Deevsalar;R. Shinjo;M. Ghaderi;M. Murata;P. Hoskin;Shoma Oshiro;Kuo‐Lung Wang;Hao-Yang Lee;I. Neill
中科院分区：
文献类型：
--
作者：
R. Deevsalar;R. Shinjo;M. Ghaderi;M. Murata;P. Hoskin;Shoma Oshiro;Kuo‐Lung Wang;Hao-Yang Lee;I. Neill
新特提斯洋俯冲到伊朗中部微大陆（CIMC）之下的后果之一是位于扎格罗斯造山带萨南达季-锡尔詹带（SaSZ）的马来耶-博鲁耶德深成杂岩（MBPC）中罕见的辉长岩侵入体的发育。 MBPC是SaSZ北部一套广泛的长英质和小镁铁质岩浆产物，具有中侏罗世（Ghorveh-Aligudarz弧）的弧状岩浆作用和晚始新世的板内型岩浆作用的地球化学特征。中侏罗统辉长岩（非堆积和堆积）具有低 Ti 浓度 (< 1 wt.%) 和相当均匀的同位素组成（初始 87Sr/86Sr：0.7035–0.70593 和 εNd(t)：− 6.18 至 − 0.7），相对于 HFSE 富集 LILE，轻稀土元素和重稀土元素之间的可变分馏((La/Yb)cn: 2.27–7.45) 且均为负到正 Eu 异常。弧型岩浆作用的这些独特特征与这些岩石的俯冲改变地幔源相一致。微量元素和 REE 模型表明，弧下地幔楔中含有角闪石的交代石榴石-尖晶石二辉橄榄石（石榴石：尖晶石 ~ 7:3）熔化了约 15%。堆积辉长岩和非堆积辉长岩属于共同液体谱系，具有互补的微量元素模式。样品之间的大部分差异可以通过共同母体的分级结晶（FC）来模拟；该套件中只有一颗累积辉长岩显示出污染的同位素证据，可能是由贫铷地壳材料造成的。晚始新世辉长岩的 Ti 含量相对较高 (> 1 wt.%)，并显示出同位素贫化的 Sr–Nd 值（初始 87Sr/86Sr：0.7044–0.7087，εNd(t)：1.9 –+3.2，除非有一个地壳污染的样品）。类似 OIB 的微量元素特征，例如富集的 HFSE，以及仅少量富集的 LILE 和 LREE，反映了板内特征和软流圈来源。微量元素模型表明，上地幔二辉橄榄岩（石榴石：尖晶石 ~ 3:1）发生小程度熔融（熔炼：0.05），随后在较浅深度（石榴石：尖晶石 ~ 4.5:2）发生较高程度熔融（熔炼：0.15）。始新世母岩浆经历了橄榄石和单斜辉石的FC。我们认为，始新世软流圈上升是由板片回滚引起的板片撕裂引发的，据报道，这在伊朗各地引发了与扩张相关的岩浆活动的“爆发”。 N-SaSZ 的 Ghorveh-Aligudarz 弧段构造岩浆演化的三个阶段表现为：1）中侏罗世新特提斯海道活跃俯冲期间的弧状岩浆作用，2）白垩纪-古新世浅角或高倾斜俯冲期间的岩浆静止，3）前不久板片撕裂期间的软流圈熔融。阿拉伯-欧亚大陆碰撞的爆发。
One of the consequences of Neo-Tethys ocean subduction beneath the Central Iranian Micro-continent (CIMC) is the development of rare gabbroic intrusions in the Malayer–Boroujerd Plutonic Complex (MBPC) located in the Sanandaj–Sirjan Zone (SaSZ) of the Zagros Orogenic belt. The MBPC is a suite of extensive felsic and lesser mafic magmatic products in the northern SaSZ with geochemical signatures of arc-like magmatism during the Middle Jurassic (Ghorveh–Aligudarz arc) and intraplate type in the Late Eocene. Middle Jurassic gabbros (non-cumulate and cumulate) have low-Ti concentrations (< 1 wt.%) and quite uniform isotopic compositions (initial87Sr/86Sr: 0.7035–0.70593 and εNd(t): − 6.18 to − 0.7), enriched LILE relative to HFSE, variable fractionation between the LREE and HREE ((La/Yb)cn: 2.27–7.45) and both negative to positive Eu anomalies. These distinctive features of arc-type magmatism are consistent with a subduction-modified mantle source for these rocks. Trace element and REE models indicate ~ 15% melting of a metasomatized amphibole-bearing garnet-spinel lherzolite (garnet:spinel ~ 7:3) in the sub-arc mantle wedge. The cumulate gabbros and non-cumulates belong to common liquid line of descent, with complementary trace element patterns. Much of the variation between samples can be modeled by fractional crystallization (FC) of a common parent; only one cumulate gabbro from this suite exhibits isotopic evidence of contamination, probably by Rb-depleted crustal materials. The Late Eocene gabbros have relatively high-Ti (> 1 wt.%) and display isotopically depleted Sr–Nd values (initial87Sr/86Sr: 0.7044–0.7087, εNd(t): 1.9 –+3.2, barring one crustally-contaminated sample). OIB-like trace element characteristics such as enriched HFSE, and only minor enrichment of LILE and LREE, reflect a within-plate character and asthenospheric source. Trace element modeling indicates small degree melting (fmelting: 0.05) of upper mantle lherzolite (garnet:spinel ~ 3:1) followed by higher degree melting (fmelting: 0.15) at shallower depths (garnet:spinel ~ 4.5:2). The Eocene parental magma underwent FC of olivine and clinopyroxene. We propose that Eocene asthenospheric upwelling was triggered by slab tearing in response to slab-rollback, which is elsewhere reported to have triggered a ‘flare-up’ of extension-related magmatism across Iran. Three stages of tectono-magmatic evolution in the Ghorveh–Aligudarz arc segment of the N-SaSZ are represented by: 1) arc-like magmatism during active subduction of the Neo-Tethys seaway at Middle Jurassic, 2) magmatic quiescence during an interval of shallow-angle or highly oblique subduction during the Cretaceous–Paleocene, and 3) asthenosphere melting during slab tearing shortly before the onset of the Arabia–Eurasia collision.